HONG KONG, June 17 (Reuters) - Opportunistic or a testament to its strong ties, balance sheet and global M&A profile?

Of the dozen or so banks involved in miner Rio Tinto's (RIO.AX)(RIO.L) year-long takeover saga, only JPMorgan (JPM.N) has served three different roles to two separate clients.

JPMorgan showed its muscle as it switched sides during the Rio deal, but also raised some eyebrows.

The bank's swift move from advising Chinese client Chinalco on its $19.5 billion offer for Rio assets and a doubling of its stake in the miner to helping Rio underwrite a bumper rights issue has prompted rival bankers to query JPMorgan's loyalties.

The New York bank, Rio's corporate broker in London via affiliate JPMorgan Cazenove, advised the Anglo-Australian miner in fending off a hostile bid by rival BHP Billiton (BLT.L) (BHP.AX) that collapsed late last year.

It then gained a last-minute advisory role for Aluminum Corp of China (Chinalco), helping the state-backed metals company as it sought to buy into Rio Tinto.

Rio eventually ditched that plan, opting instead for a $15.2 billion rights issue and an iron ore joint venture with BHP. One of the underwriters mandated for the rights offer: JPMorgan.

JPMorgan's flip-flopping between clients breaks no rules, and some rival investment bankers say its manoeuvring is a credit to its business relationships, financial muscle and top status in the global M&A advisory league tables.

Others say it may put itself in an awkward position -- even though the bank's latest mandate with Rio is for securities underwriting and not M&A advice.

Both JPMorgan and Chinalco declined to comment for this article. The sources declined to be named because they were not authorised to speak publicly on the matter.

RELATIONSHIP BANKING

JPMorgan's relationship with Chinalco goes back several years. It was one of the bookrunners for Chalco's (2600.HK) (601600.SS) around HK$4.5 billion share placement in May 2006. Chinalco is the parent of Chalco.

With JPMorgan among those defending Rio from the BHP offer, the bank did not take part in Chinalco's 'dawn raid' last year in which it purchased a stake in Rio in a bid to block BHP.

But, two months after that bid fell through, JPMorgan was invited in to advise Chinalco as it sought to capture Rio assets and shares at the bottom of the commodity price cycle -- a deal that would have helped Rio pay down its huge debts.

Chinalco was already being advised by Japanese bank Nomura (8604.T) -- a legacy relationship through Lehman Brothers -- Blackstone Group (BX.N) and China's CICC.

The late addition of JPMorgan didn't sit well with the other bankers, sources say, and that discomfort has only grown now that JPMorgan is in a position to earn a hefty fee as a Rio underwriter following the collapse of the Chinalco offer.

This happens in investment banking. Even if executives on both sides agree to a client relationship, competitors will see the potential for a conflict of interest.

The key to navigating these issues is the comfort level of the bank's client, says Jamie Allen, secretary general of the Asian Corporate Governance Association, speaking generally about corporate governance.

"But I guess they would need to make sure their investment bank isn't advising the other side on doing something differently," he said. "Presumably, it would be different teams within the investment bank, but that isn't entirely a cause for comfort."

While some say a financially strong JPMorgan is being opportunistic, others note that Chinese corporate clients are growing more savvy and an adviser's other business interests is far less of an issue there than in the United States or Europe.

"It's a strategic business decision that each bank has to make for itself," said a Hong Kong-based M&A lawyer, referring to JPMorgan's role in the deals.

"Presumably, part of the analysis is how the decision would play with the guy on the other side, who may be a client in another context. In the end, they've got to live with their decision." (Editing by Ian Geoghegan)